I've found this design to be more effective than the semi-circular and fully circular fan nozzles. This is a re-design of the stock fan nozzle that shipped with the printer. I've removed some unnecessary arcs and curves and opted for a pretty direct reduction to a 2.4mm opening. Since I installed it I've found my prints to be way smoother with more even cooling.
The walls are thin enough for a 100% infill. And I've kept everything to a nice multiplier of my nozzle width (0.4). My printer and filament I'm using are decent enough to span the small-ish overhangs for a smooth print (other than the overhang on the fan housing insert).
Filament used: KCamel Silver (slightly translucent) PLA